During the director/actor commentary of Amazing Grace Benedict was mentioned a few times.

Michael Apted (MA): ...Benedict Cumberbatch, this is his first really big role, and what was so interesting, meeting him, was just like Wilberforce comes from a trading community, it was important that William Pitt came from nobility, and as soon as Benedict walked in, 你 knew,Ioan Gruffudd (IG): Immediately. Yes, he has that sort of quality about him.MA: He has class. IG: Absolute class. Classy guy. Absolutely.MA: It's hard to act that sort of stuff. So when I was doing all this casting, it was sort of...